When making improvements around the home landscape, you may need to backfill an area with fill dirt. Determining the right volume formula for your project depends on the shape of the area to be filled. For a rectangular-shaped area, you would multiply the three dimensions. Circular shapes require you to use the geometric value pi in your formula. The main thing to remember is that all your measurements must be in the same units. If you take your measurements in inches, it will be easy to convert to cubic yards, the volume unit dirt is sold by.

Rectangular Area

Measure the length, width and depth of the area you want to fill with dirt. Record your dimensions in inches. For example, suppose that the length is 10 feet (120 inches), width is 5 feet (60 inches), and depth is 2 feet 6 inches (30 inches).

Calculate the volume of dirt needed to fill the area you measured by multiplying length (120 inches) by width (60 inches) by depth (30 inches). Total volume equals 216,000 cubic inches.

Circular Area

Measure the diameter and depth of the hole you want to fill with dirt. Record your measurements in inches. For this example, suppose that the hole you will fill is 5 feet (60 inches) in diameter and 2 feet 6 inches (30 inches) deep. The radius of 5 feet is 2.5 feet (30 inches).

Calculate the volume of dirt needed to fill in the hole using pi (3.142) times the square of the radius times the depth. For this example, you would multiply 3.142 by the square of 30 by 30 to obtain the volume. This yields 3.142 times 900 inches times 30 inches, or 84,834 cubic inches.

Convert 84,834 cubic inches to cubic yards by dividing by 46,656 cubic inches. It will require 1.82 cubic yards of dirt to fill in the hole.

Things You Will Need

Tape measure

Calculator

Tip

If your measurements are in feet, you can convert cubic feet to cubic yards by dividing cubic feet by 27 cubic yards.

Things Needed

Tape measure

Calculator

Tips

If your measurements are in feet, you can convert cubic feet to cubic yards by dividing cubic feet by 27 cubic yards.

About the Author

Diana K. Williams is a certified Master Gardener, has more than a decade of experience as an environmental scientist, and holds a Bachelor of Science degree in biology and environmental studies from the Ohio Northern University. Williams is a winner of Writer’s Digest Magazine's annual writing competition.